Machine tools that removal-machine a part of a workpiece by a tool are widely known in the related art. In such machine tools, when the workpiece is machined, the tool is pressed against the workpiece while a part of the workpiece is retained by a retaining device such as a workpiece spindle device.
In this process, there may be cases where a part of the workpiece is deflected due to a force of the tool pushing the workpiece. When the workpiece is deflected, machining precision is inevitably reduced. Thus, in order to prevent the deflection of the workpiece, in the related art, there has been proposed provision of a support device which supports the workpiece, separately from the workpiece spindle device.
For example, JP 2010-264562 A discloses a machining system in which ends of the workpiece are supported by an end supporting means, and an intermediate part of the workpiece is supported by an intermediate part supporting means. In this machining system, a position of the workpiece is measured with a sensor, and a workpiece support position in the up-and-down direction by the intermediate part supporting means is adjusted based on the measurement result, so that height positions of the ends and the intermediate part of the workpiece are the same. According to such a technique, deflection can be prevented for various workpieces having different shapes, and the machining precision can be further improved.
In the support device of the related art, however, the support point (workpiece support position) is controlled by position control. That is, a position of a support point is measured by a sensor or the like, and the support point is moved and controlled so that the measurement result matches a target value. However, in order to appropriately support the workpiece by such position control, a high level of positioning precision is required. In order to highly precisely position the support point, it is necessary that the support device to be controlled itself has a high rigidity. This is because, when the support device has a low rigidity and the support device is deflected, a control error would be increased. However, when the rigidity of the support device is to be increased, problems may arise such as an increase in size and cost of the support device.
An advantage of the present disclosure lies in provision of a machine tool which can appropriately support a workpiece even when the support device has a low rigidity.